Cryogenic ultra-high power infrared diode laser bars

Progress in high-energy-class diode laser pump sources

“…Contact via copper foil enables many different bar geometries to be rapidly assessed, but adds additional packaging resistance of R p ~ 200 µΩ, comparable to the resistance of the bar itself, R. The copper plate contact reduces R p to ~ 10 µΩ. For studies into improved bar performance, copper foil contact is typically used for lower cost and faster and more flexible assembly, with R p subtracted after testing to reveal the performance of the bar itself, at the risk of introducing errors if R p varies [10]. At DILAS, LDA packaged QCW bars are a standard product, with state of the art power and efficiency, based on commercial diode laser bars with L = 1.5...2.0 mm [4][5]8].…”

“…1. At the FBH, two different gold-plated copper heatsinks were used, termed CCPs or CS-mounts [10]. The diode laser bars are first mounted junction side down with hard solder between two expansion-matched CuW carriers, which are then mounted onto the CCP.…”

“…Diode lasers were first fabricated following standard techniques [10] using a baseline epitaxial design, to form laser bars with resonator length L = 4 mm, that contained 45 single emitters with width W = 100 µm resulting in F = 45%. The vertical epitaxial design was grown using MOVPE techniques and used a 2.2 μm thick waveguide and a single InGaAs quantum well for operation at T HS = 25°C with λ op = 940 nm, as previously presented in [12].…”

“…However, this improved power must be delivered without compromised lateral and vertical far field angle (Θ L 95% and Θ V 95% respectively, with 95% power content) and spectral width (Δλ 95% , with 95% power content), which must be suitable for combining into a pump system. In recent studies at the Ferdinand-Braun-Institut (FBH), higher P op has been demonstrated at heat sink temperatures of T HS = 25°C in both single emitter [9] and bar format [10], specifically at P op > 1 kW per 1 cm aperture. In these studies, large resonator lengths L = 6 mm were used to minimize diode electrical resistance R so that η E can be sustained to the highest powers.…”

“…Therefore, it would be attractive to also cool the diode laser pump sources, if the performance gains are sufficient to justify the extra complexity. Therefore, the FBH is also performing device and technology development, seeking to leverage T HS = -70°C to deliver highest possible diode laser bar performance [10]. These studies are performed on 1 cm laser bars, as anticipated to be needed for the largest high-energy-class laser systems [1][2][3].…”